1. Field of the Invention
The present invention relates to a light emitting element material, amine compound, and organic light emitting element using the light emitting element material and amine compound, which are used for a flat surface light source and display, and more specifically, to a light emitting element material, amine compound, and light emitting element using the light emitting element material and amine compound which, with application of low voltage, can emit light ranging from green to red with high luminance and high efficiency.
2. Description of the Related Art
An organic light emitting element in which an organic material is used (hereinafter, referred to upon occasion there is a case in which it is referred as “an organic EL element”) is promising for applications as an inexpensive large area full-color displaying element of a solid light emitting type, and various development thereof has been carried out in recent years. Generally, an organic light emitting element is formed by a light emitting layer and a pair of opposing electrodes which nip the light emitting layer therebetween. Light emission by the organic light emitting element is a phenomenon in which, in a case in which an electronic field is applied between the pair of electrodes which nip the light emitting layer, electrons are injected from a cathode, while positive holes are injected from an anode, and these electrons and positive holes are bound once again at the light emitting layer. An energy gap generated when energy level returns from a conduction band to a valence electron band is emitted as light.
Conventional organic light emitting elements have high driving voltage and also have low light emission luminance and light emission efficiency. However, in recent years, an organic EL element formed by laminating a thin film containing an organic compound having high fluorescent quantum efficiency and emitting light with application of low voltage of 10 volts or less has been reported (Applied Physics Letters, vol. 51, p. 913, 1987) and has gathered attention. The method of preparing the organic EL element uses a metal chelate complex as an electron transporting layer, a fluorescent band layer as a light emitting layer, and an amine compound as a positive hole transporting layer, to obtain a light emitting element having a green light emitting characteristic with high luminance. On the other hand, in consideration of a case in which the organic EL element is used in a full color display and a light source, practically, it is required to have the organic light emitting element emit light of three primary colors or white light. As a method of having the organic light emitting element emit light of a desired color, a method in which a fluorescent dye is doped on a light emitting layer or the like to have the organic light emitting element emit light of a desired color has been reported (Journal of Applied Physics, vol. 65, p. 3610, 1989). This method is effective particularly for red light emission. With red light emission, it is difficult to use a single fluorescent dye as a light emitting layer due to significant density quenching. This method is useful in terms of accomplishing satisfactory color purity and high luminance. However, there is a problem with this method that, in a case in which an element on which a dye has been doped by vapor deposition is produced, a host material and a very small quantity of the fluorescent dye must be vapor-deposited together so that the operation thereof is troublesome. Further, inconsistency in performance of the manufactured organic light emitting element is liable to occur. Therefore, in view of simplification of the manufacturing process and stabilization of the performance of elements, development of a light emitting material which has a satisfactory color purity and which can be used as a light emitting layer by itself, and particularly, development of a red light emitting material which accomplishes satisfactory chromaticity and luminance even if it is used as a light emitting layer by itself, has been desired.
On the other hand, in terms of organic EL elements, an element which is laminated on the organic material by vacuum deposition achieves high luminance light emission. However, in view of simplification of manufacturing process, workability, expansion of the area and the like, it is desirable to produce the element by a coating method. However, an element which is produced by a conventional coating method is inferior to an element which is produced by a vapor deposition method in terms of light emission luminance and light emission efficiency. Light emission with high luminance and high efficiency is a significant issue. As the coating method, there is a method in which an organic low molecular compound which is a light emitting element is applied dispersedly on an organic polymer medium. However, with the light emitting element produced in such a way, there is a problem that, in a case in which the light emitting element emits light for a long period, due to aggregation of an organic low molecular compound or the like, uniform sheet light emission gradually becomes difficult.
Moreover, in recent years, for a dye for a filter, color conversion filter, dye for photographic photosensitive material, sensitizing dye, dye for pulp dyeing, laser dye, fluorescent medicament for medical diagnosis, and material for an organic light emitting element and the like, various materials which have fluorescent characteristics have been used, and demand therefor has increased. However, there is only a small variety of red fluorescent dyes which have strong fluorescent intensity and high color purity, and development of a new material has been desired.